"The villain is Ben Sisko."
Sent back by the Prophets or escaped, with a very different attitude than he had before (which would be later if time was linear, but it's not) and determined to find a way to stop the Dominion war before it begins and/or make sure the Cardassians never invade Bajor, for the good of the Bajorans and the Federation. But no one listens to him and he has to use unwelcome tactics to achieve his goals.
Damn I'm stupid! But that's a good way to remember DS9!